Differential servo-limiter

ABSTRACT

A differential servo-limiter for regulating flow in hydraulic circuit employs an electromagnet which acts when energized on the same side of a throttle as restricted pressure from the inlet to the differential servo-limiter to balance the pressure difference acting on the other side of the throttle valve constituting unrestricted inlet pressure, the residual flow going to the outlet being at all times dependent on the intensity only of the current to the solenoid coil.

United States Patent Bourgeois [S4] DIFFERENTIAL SERVO-LIMITER [72] Jacques Bourgeok, Paris, France [73] Societe a Responsabilite Limitee dite Seram, Livry-Gargan, France Filed: Oct. 22, 1970 App]. No.: 82,917

Foreign Application Priority Data Oct. 22, 1969 France ..6936l53 US. Cl ..137/501, 267/182 Int. Cl. ..F16k 31/12 Field of Search ..137/500, 501, 503; 267/182 References Cited UNITED STATES PATENTS 3,502,100 3/1970 Jonson ..137/501X Inventor:

Assignee:

[l5] 3,680,586 [4 1 Aug. 1,1972

3,024,798 3/1962 Banker ..137/501 X 3,223,115 12/1965 Kates ..l37/501 Primary Examiner-Henry T. Klinksiek AttorneySughrue, Rothwell, Mion, Zinn & Macpeak [57] ABSTRACT A differential servo-limiter for regulating flow in hydraulic circuit employs an electromagnet which acts when energized on the same side of a throttle as restricted pressure from the inlet to the differential servo-limiter to balance the pressure difference acting on the other side of the throttle valve constituting unrestricted inlet pressure, the residual flow going to the outlet being at all times dependent on the intensity only of the current to the solenoid coil.

4 Claim, 1 Drawing Figure 7 I II/lllll/IIIIIIIIIIIIIIllIIIl/dllItIlI/IIIIII III I DIFFERENTIAL SERVO-LIMITER Hydraulic servo-limiters with electrical regulation are known which are apparatus controlled by solenoid means wherein the adjustment effected by the servolimiter is proportional to the intensity of the supply current. Such apparatus, mounted on a hydraulic circuit, between an upstream pressure P and, for example, the discharge, permit of regulating the pressure P to a given value in accordance with the intensity applied to the solenoid.

On the other hand, hydraulic pressure reducers are known which are apparatus wherein the residual pressure obtained from an upstream pressure P is dependent on the calibration of a spring.

It is possible, by combination of two apparatus of this kind, to provide a flow regulation for example by collecting a constant residual pressure P,, from a variable pressure P, through a pressure reducer; then applying this constant residual pressure P, to a calibrated orifice or diaphragm introducing into the fluid flow a pressure loss p and connecting downstream of the calibrated orifice a servo-limiter of the type described hereinbefore permitting of varying the pressure from O to P,, assuming that it is connected downstream to the discharge, in accordance with the intensity applied to the solenoid of the servo-limiter, and bringing about in fact a flow regulation which is proportional to the pressure loss p in the calibrated orifice given a suitable choice of the latter. Such a combination has the disadvantage of being expensive to construct since it uses two different apparatus.

The object of the invention is to obtain a specific flow rate in a hydraulic circuit in a simpler and less expensive manner with at least as much precision as by the combination discussed hereinbefore, and by means of a single apparatus.

The invention provides an apparatus which will be referred to hereinafter as a differential servo-limiter, which is characterized in that it comprises in combination essentially:

a first portion provided with a central chamber containing a mobile throttle valve,

a second portion, mounted in sealing-tight manner on the first, consisting chiefly in a solenoid provided with a central cavity in which there is adapted to move a plunger core acting through the agency of a push rod on the valve of the first portion,

a first hydraulic circuit putting the supply on the one hand into direct and permanent communication with a first side of the central chamber of the first portion in which the valve moves, on the other hand into permanent communication through the agency of a calibrated orifice both with the second side of the central chamber of the first portion in which the valve moves and with the central cavity of the second portion in which the plunger core of the solenoid moves,

a second hydraulic circuit, establishing communication between the user and the second side of the central chamber of the first portion, depending on the position of the throttle valve in the said chamber, the said valve creating a pressure loss which, from one position of equilibrium to the other, varies as the difi'erence in pressures between the supply and the user varies.

The invention will be readily understood by the description of one preferred form of embodiment given by way of non-limitative example, with reference to the accompanying drawing which shows the said form of embodiment in sectional view.

In the apparatus shown in the accompanying drawing, a fluid under pressure P, is introduced through the supply orifice la or 1b selectively.

From there, it passes directly and permanently, through the lateral orifice 6 in a sleeve 25, into the first side of a central chamber 2 containing a valve 3. The chamber 2 is closed towards the exterior by a plug 4 and the pressure P, tends to displace the valve by action on the surfaces 8, and S thereof, one surface, an annular surface, appearing in section in the drawing in the form of the shoulder 5, and the other, a circular surface, corresponding to the end 7 of the valve. The movement of the valve is counteracted by a solenoid 8 comprising in addition to the magnetic circuit a coil 9 which is supplied with current through a terminal 10 and a plunger core 11 which moves in a central cavity 16 of which it has substantially the same cross-section and acting on the valve 3 by means of a push rod 12 made of a non-magnetic material. The solenoid 8 is itself mounted in sealing-tight manner by means of a sealing ring 15 on a base 14 made of a magnetic material, closing the magnetic circuit of the solenoid, and in this base there is formed a central passage 13 for a push rod 12.

The fluid under pressure P applied to the admission orifice 1a or lb, at the same time as it enters directly through the access orifice 6 into a first side of the chamber 2, passes into the solenoid by way of ducts l7, 18 formed opposite one another respectively in the body 20 of the apparatus and the base 14 of the solenoid, which is mounted on the said body 20 in sealingtight manner by means of the sealing ring 19.

Between the admission orifice 1 and the duct 17 there is situated a calibrated orifice 24 introducing a pressure loss p into the fluid flow towards the second side of the central chamber 2, in which the valve moves. The fluid, after passing through the calibrated orifice 24, the ducts 17, 14 and the winding of the solenoid 9, is introduced on the one hand at the summit of the plunger core 11 into the central cavity 16 and on the other hand at the other end of the plunger core into the same cavity, for example, passing through a bore, a groove or any other communication formed in or on the plunger core and illustrated in the drawing in the form of broken lines 21.

From the duct 17, formed in the body 20 of the apparatus, the fluid coming from the orifice l flows on the other hand into the central chamber 2 at the side of the valve 3 opposite from the first side receiving the fluid introduced directly through the orifice 6 under the pressure P Finally, orifices 22 formed in the sleeve 25 establish communication, according to the position of the valve 3, between this same portion of the chamber 2 and an external orifice 23a or 23b connected to the user or to the discharge under the pressure P,.

The apparatus operates as follows:

For a specific intensity applied to the solenoid, the

' plunger core 11 by means of the push rod 12 exerts a pressure F on the valve 3 which is proportional to the said intensity.

Since the fluid applied to the orifice 1 under pressure P, undergoes a pressure drop p in passing through the calibrated orifice 24, a pressure P p is established in the central cavity 16 of the solenoid. Since the fluid fills this cavity both at one side of the plunger core 11 and at the other owing to the communication 21 the push rod 12 is subjected not only tothe pressure F of the plunger core but also to a force (P p)s, s being the cross-section of the push rod 12.

In the portion of the chamber 2 which, by way of the orifice 6 is in direct communication with the fluid under pressure P the valve is subjected to a pressure P,(S S,), S, and S, being the respective cross-sections of the end of the valve and of the annulus which permits permanent access of the fluid into this first portion of the chamber 2.

In the opposite portion of the chamber 2 there prevails the pressure P p and the valve is subjected on the one hand to the pressure of the push rod F (P p)s, and also to that of the fluid situated in the second portion of the chamber 2, (P, p)(S, S s). In fact the cross-section of the valve on which the fluid exerts its pressure is equal to the total section of the valve (S 8,) minus that of the push rod s.

When the valve is in a state of equilibrium, there is equality between the forces which act on it at both sides, nam'ely:

In other words, by making the fluid communicate with the central cavity of the solenoid, a hydraulic pressure is obtained on the second side of the valve which is independent of the existence of the push rod.

Moreover, in the general equilibrium of pressures there is the equation: P P, p Ap (2), wherein P, is the pressure of use or the discharge pressure at the orifice 23 and Ap is the pressure drop created by the throttling of the orifices 22 by the valve 3 and dependent on the position thereof. It will be seen that any increase in the difference P P, results in a supplementary force supplied to the lower portion of the throttle valve 3, and therefore a lifting of this valve 3 and a reduction in the cross-section of passage through the orifices 22, that is to say an increase in the pressure drop Ap.

From one position of equilibrium of the valve to the other, the pressure drop Ap varies as the difierence in the pressures P P, varies, whilst the pressure drop p created by the calibrated orifice 24 remains constant and proportional to the force F exerted on the valve by the solenoid as is shown in the equation (1), that is to say proportional to the intensity i applied to the said solenoid.

Thus, the flow rate of the fluid through the calibrated orifice 24, which is solely dependent on the value of p, is solely dependent on the intensity applied to the solenoid and, by the differential servo-limiter according to the present invention the flow rate of a hydraulic circuit is optionally regulated in accordance with the intensity applied to the solenoid.

Of course the invention is in no way limited to the form of embodiment described and illustrated which has been given simply by way of example. More particularly it is possible to make modifications to details and to replace certain means by equivalent means without departing from the framework of the invention.

lFk tiifferential servo-limiterfor regulating the flow of pressurized fluid in a hydraulic circuit, said limiter compnsmg:

first and second parts coupled together in a sealing type manner, said first part including a central chamber containing a slidable throttle valve sealably carried therein, and said second part com prising means, mounted in a sealing type manner on said first part, for actuating said throttle valve, openings in said first part for delivering without fluid restriction, the inlet pressure of the hydraulic circuit to one side of the throttle valve, calibrated means for delivering a restricted fluid pressure to the other side of said throttle valve fromsaid inlet, 1

means for leading the restricted pressure from the other side of said throttle valve to the outlet, and wherein said means for actuating said throttle valve comprises an electromagnet acting, when energized, in conjunction with said restricted fluid pressure on the same side of said throttle valve and balancing the unrestricted fluid pressure acting on the other side of the throttle valve; whereby, the residual flow passing to the outlet at all times is dependent upon the intensity of the current applied core to said throttle valve and being provided on the other hand with a lateral bore providing passage for restricted fluid pressure between said first and second parts. a

3. The differential servo-limiter as claimed in claim 1, wherein said plunger core of said electromagnet includes fluid communication means pemiitting hydraulic pressurized fluid to fill the central cavity of the electromagnet and provide equal pressure at each end of the plunger core.

4. The differential servo-limiter as claimed in claim 1, in which the throttle valve comprises at one end, an annular shoulder permitting permanent access of the unrestricted inlet pressure to that end of the chamber in which the valve moves. 

1. A differential servo-limiter for regulating the flow of pressurized fluid in a hydraulic circuit, said limiter comprising: first and second parts coupled together in a sealing type manner, said first part including a central chamber containing a slidable throttle valve sealably carried therein, and said Second part comprising means, mounted in a sealing type manner on said first part, for actuating said throttle valve, openings in said first part for delivering without fluid restriction, the inlet pressure of the hydraulic circuit to one side of the throttle valve, calibrated means for delivering a restricted fluid pressure to the other side of said throttle valve from said inlet, means for leading the restricted pressure from the other side of said throttle valve to the outlet, and wherein said means for actuating said throttle valve comprises an electromagnet acting, when energized, in conjunction with said restricted fluid pressure on the same side of said throttle valve and balancing the unrestricted fluid pressure acting on the other side of the throttle valve; whereby, the residual flow passing to the outlet at all times is dependent upon the intensity of the current applied to the electromagnet solenoid.
 2. The differential servo-limiter as claimed in claim 1, wherein said electromagnet is formed of an upper element which comprises said solenoid and its plunger core, and a lower element made of magnetic material and serving as a base for the solenoid, said lower element being maintained in sealing tight manner on said upper element and being provided on the one hand with a control hole permitting passage of the push rod for transmitting movements of the solenoid plunger core to said throttle valve and being provided on the other hand with a lateral bore providing passage for restricted fluid pressure between said first and second parts.
 3. The differential servo-limiter as claimed in claim 1, wherein said plunger core of said electromagnet includes fluid communication means permitting hydraulic pressurized fluid to fill the central cavity of the electromagnet and provide equal pressure at each end of the plunger core.
 4. The differential servo-limiter as claimed in claim 1, in which the throttle valve comprises at one end, an annular shoulder permitting permanent access of the unrestricted inlet pressure to that end of the chamber in which the valve moves. 